LLM Critic: User-friendly on_fail messages

[rkritika1508]

Is your feature request related to a problem?
When using the LLM Critic validator with the rephrase on_fail action, the response provided is not user-friendly. It presents technical details instead of a clear message, which can confuse users.

Describe the solution you'd like

• Provide a user-friendly response for all on_fail actions in LLM Critic.
• Ensure that messages are clear and understandable, rather than technical.

Original issue

Describe the bug
A clear and concise description of what the bug is.
When using the LLM Critic validator, if we use the rephrase on_fail action, we don't receive a user-friendly response. It's something like -

{
"success": true,
"data": {
"response_id": "30a0c27c-8cab-43dc-b5e0-b023dffa98e9",
"rephrase_needed": true,
"safe_text": "Please rephrase the query without unsafe content. The response is missing or has invalid evaluations for the following metrics: ['query']."
}
}

Instead, we should have a user friendly response for all on_fail actions.

To Reproduce
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4. See error

Expected behavior
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Additional context
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